Exhaust heating apparatus for internal combustion engine and control method for the same

ABSTRACT

An exhaust heating apparatus ( 37 ) according to the present invention, for heating exhaust being led to an exhaust emission purifier ( 30 ) from an internal combustion engine ( 10 ) in which a first exhaust turbocharger ( 28 ) and a second exhaust turbocharger ( 29 ) that is mainly used in a lower rotational speed range of the engine than the first turbocharger are incorporated, is arranged in a first exhaust passage ( 26   f ) that is located further upstream than a confluent portion ( 27   c ) of the first exhaust passage, which passes through an exhaust turbine ( 28   b ) of the first turbocharger and continues to the exhaust emission purifier, and a second exhaust passage ( 26   s ), which goes around the exhaust turbine of the first turbocharger and passes through an exhaust turbine ( 29   b ) of the second turbocharger and continues to the exhaust emission purifier, and further downstream than the exhaust turbine of the first turbocharger.

TECHNICAL FIELD

The present invention relates to an exhaust heating apparatus thatincreases a temperature of exhaust in order to activate an exhaustemission purifier and keep the exhaust emission purifier in an activatedstate in an internal combustion engine that is provided with the exhaustemission purifier.

BACKGROUND ART

A turbocharger that comparatively easily achieves an improvement inoutput from an internal combustion engine also has a tendency at thesame time to bring about a drop in fuel efficiency. In recent years, inorder to meet the strong demand for an improvement in the fuelefficiency of internal combustion engines in which this kind ofturbocharger is incorporated, internal combustion engines in which twoturbochargers having different characteristics are incorporated areproposed in Patent Literature 1 and Patent Literature 2. In either case,there are provided a first turbocharger that mainly functions in a lowrotational speed range of the internal combustion engine, and a secondturbocharger that mainly functions in rotational speed ranges other thanthat; and these turbochargers are arranged in series or parallel in theintake and exhaust passages.

Meanwhile, coping with strict emission standards set on internalcombustion engines has lead to a necessity for facilitating theactivation of an exhaust gas purifying device at the start of itsinternal combustion engine, maintaining its active state during theoperation of the internal combustion engine, and so on. In this respect,Patent Literature 1 and the like have proposed internal combustionengines in which an exhaust gas heating device is installed upstream ofan exhaust gas purifying device in an exhaust passage. This exhaust gasheating device generates heating gas within exhaust gas and suppliesthis generated heating gas into the exhaust gas purifying device givenat the downstream side to thereby facilitate the activation of theexhaust gas purifying device and maintain its active state. To do so,the exhaust gas heating device generally includes a fuel supply valvewhich adds fuel into the exhaust passage, and an igniter such as a glowplug which heats and ignites the fuel to generate heating gas.Furthermore, there is also known an exhaust heating apparatus in which acompact oxidation catalyst is arranged in the exhaust passage further onthe downstream side than the igniter in order to increase thetemperature of the heated gas. This oxidation catalyst has a heatgeneration function of its own, and has a function for reforming fuel toa low-carbon component, however, has different structure than theoxidation catalyst that is used as part of the exhaust emissionpurifier.

CITATION LIST Patent Literature

[Patent literature 1] Japanese Patent Laid-Open No. 2008-255902

[Patent literature 2] Japanese Patent Laid-Open No. 2009-270470

[Patent literature 3] Japanese Patent Laid-Open No. 2006-112401

SUMMARY OF INVENTION Technical Problem

It is evident that in the future, an internal combustion engine that isable to achieve both good output characteristics and fuel efficiency andclean exhaust will be important technology, and from this aspect, it hasbeen considered that an exhaust heating apparatus is furtherincorporated in an internal combustion engine in which two-stage exhaustturbochargers as described above is incorporated.

In an exhaust heating apparatus disclosed in Patent Literature 3, in thecase of an operating state where an intake flow related to an internalcombustion engine is large, a flow rate of exhaust that flows through anexhaust passage also relatively increases. Therefore, it is not possiblefor fuel that is supplied to the exhaust passage from a fuel supplyvalve of the exhaust heating apparatus to remain around the igniter, andeven when ignited, the flame is blown out by the flow of the exhaust, sothere is a possibility that fuel that has not been combusted will flowtoward the exhaust emission purifier side.

On the other hand, in the internal combustion engine in which the2-stage exhaust turbochargers are incorporated, there is basically atendency for an exhaust flow to become large. Moreover, the exhaustpasses through exhaust turbines of the two turbochargers, respectively,so a temperature of the exhaust greatly drops due to the release of theheat to the outside and a heat capacity of the exhaust turbinesthemselves. As a result, the troubles described above become even moreprominent, and it may only be possible to actuate the exhaust heatingapparatus when there is a small amount of exhaust flow, such as when avehicle decelerates.

An object of the present invention is to provide an exhaust heatingapparatus that is capable of stably and continuously igniting fuel in aninternal combustion engine in which 2-stage exhaust turbochargers areincorporated.

A first aspect of the present invention is an exhaust heating apparatusfor heating exhaust being led to an exhaust emission purifier from aninternal combustion engine in which a first exhaust turbocharger and asecond exhaust turbocharger are incorporated, the second turbochargerbeing mainly used in a lower rotational speed range of the engine thanthe first turbocharger, wherein the exhaust heating apparatus isarranged in a first exhaust passage that is located further upstreamthan a confluent portion of the first exhaust passage, which passesthrough an exhaust turbine of the first turbocharger and continues tothe exhaust emission purifier, and a second exhaust passage, which goesaround the exhaust turbine of the first turbocharger and passes throughan exhaust turbine of the second turbocharger and continues to theexhaust emission purifier, and further downstream than the exhaustturbine of the first turbocharger.

In the present invention, the exhaust heating apparatus is operated inthe case of an operating state where it is not necessary to lead exhaustgas to the first exhaust passage, for example, in the case where theinternal combustion engine is in the low rotational speed range. Theresulting heated gas is merged with the exhaust flowing in the secondexhaust passage at a confluent portion of the first exhaust passage andsecond exhaust passage, and flows into the exhaust emission purifier.

In the exhaust heating apparatus for the internal combustion engineaccording to the present invention, the exhaust heating apparatus mayinclude a fuel supply valve for supplying fuel to the first exhaustpassage, and ignition means for igniting and burning fuel that wassupplied from the fuel supply valve to the first exhaust passage. Also,an oxidation catalyst is advantageously arranged in the exhaust passagebetween the ignition means and the exhaust emission purifier.

The first exhaust passage and the second exhaust passage may be arrangedin parallel between the engine and the exhaust emission purifier. Inthis case, a valve capable of adjusting a flow of exhaust that flows inthe first exhaust passage may be arranged in the first exhaust passagefurther on the upstream side than the exhaust turbine of the firstturbocharger. Furthermore, when fuel is supplied to the first exhaustpassage from the fuel supply valve, an opening of the valve may beadjusted so that the flow of exhaust flowing in the first exhaustpassage becomes less than a flow of exhaust that flows in the secondexhaust passage.

Alternatively, the second exhaust passage may be a bypass that isarranged in parallel with respect to the first exhaust passage. In thiscase, a valve capable of adjusting a flow of exhaust that flows in thebypass may be arranged in the bypass. Also, when fuel is supplied to thefirst exhaust passage from the fuel supply valve, the opening of thevalve may be adjusted so that the flow of exhaust that flows in thefirst exhaust passage becomes less than the flow of exhaust that flowsin the bypass.

A second aspect of the present invention is a control method for theexhaust heating apparatus according to the first aspect of the presentinvention that the first exhaust passage and the second exhaust passageare arranged in parallel between the engine and the exhaust emissionpurifier and that a valve capable of adjusting a flow of exhaust thatflows in the first exhaust passage is arranged in the first exhaustpassage further on the upstream side than the exhaust turbine of thefirst turbocharger, or the exhaust heating apparatus according to thefirst aspect of the present invention that the second exhaust passage isa bypass that is arranged in parallel with respect to the first exhaustpassage and that a valve capable of adjusting a flow of exhaust thatflows in the bypass is arranged in the bypass, comprising the steps ofdetecting a rotational speed of the internal combustion engine, andflowing a predetermined amount of exhaust in the first exhaust passageand actuating the exhaust heating apparatus when the detected rotationalspeed of the engine is equal to or less than a predetermined rotationalspeed, or when in an operating state where the first exhaust passage canbe closed.

In the present invention, when the internal combustion engine is in thelow rotational speed range, or when it is in the operating state wherethe first exhaust passage could be closed, the exhaust heating apparatusis operated while a valve opening is adjusted to flow a predeterminedflow of exhaust into the first exhaust passage. The resulting heated gasis merged with the exhaust flowing in the second exhaust passage at theconfluent portion of the first exhaust passage and second exhaustpassage, and flows into the exhaust emission purifier.

Advantageous Effects of Invention

With the present invention, even in an internal combustion engine inwhich 2-stage exhaust turbochargers are incorporated, it is possible tostably actuate the exhaust heating apparatus not only at the time ofdecelerating but even at the time of accelerating or traveling atconstant speed when the internal combustion engine is in the lowrotational speed range. This is the same even when in the operatingstate where the first exhaust passage can be closed. The heated gas canbe efficiently mixed with the exhaust gas flowing in the second exhaustpassage at the confluent portion with the second exhaust passage.

When an oxidation catalyst is arranged in the exhaust passage betweenignition means and the exhaust emission purifier, it is possible tofurther efficiently increase the temperature of the heated gas.

When a valve that is capable of adjusting a flow of exhaust that flowsin the first exhaust passage is arranged in the first exhaust passagefurther on the upstream side than an exhaust turbine of a first exhaustturbine type turbocharger, as long as the internal combustion engine isin the low rotational speed range, it is possible to reliably actuatethe exhaust heating apparatus. Particularly, when an opening of thevalve is adjusted so that the flow of exhaust that flows in the firstexhaust passage is less than a flow of exhaust that flows in the secondexhaust passage, it is possible to more reliably generate stable heatedgas.

Similarly, when a valve that is capable of adjusting a flow of exhaustthat flows in a bypass is arranged in the bypass, as long as theinternal combustion engine is in the low rotational speed range, it ispossible to reliably actuate the exhaust heating apparatus.Particularly, when the opening of the valve is adjusted so that the flowof exhaust that flows in the first exhaust passage is less than the flowof exhaust that flows in the bypass, it is possible to more reliablygenerate stable heated gas. Moreover, it is possible to use existingcomponents that are incorporated in the 2-stage exhaust turbochargers asa bypass and valve.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram of one embodiment of an exhaust heatingapparatus for an internal combustion engine according to the presentinvention;

FIG. 2 is a control block diagram of main components in the embodimentillustrated in FIG. 1;

FIG. 3 is a graph expressing a relationship between the engine rpm andthe turbine rpm;

FIG. 4 is a flowchart illustrating the control procedure for the exhaustheating apparatus of the embodiment illustrated in FIG. 1;

FIG. 5 is a conceptual diagram of another embodiment of an exhaustheating apparatus for an internal combustion engine according to thepresent invention; and

FIG. 6 is a flowchart illustrating a control procedure for the exhaustheating apparatus of the embodiment illustrated in FIG. 5.

DESCRIPTION OF EMBODIMENTS

An embodiment in which the present invention is applied to a compressionignition type internal combustion engine in which parallel-type 2-stageexhaust turbochargers are incorporated will be explained in detail withreference to FIGS. 1 to 4. The present invention is not, however,limited to the embodiment, and the construction thereof may be freelymodified corresponding to required characteristics. The presentinvention is effectively applied to a spark ignition type internalcombustion engine in which gasoline, alcohol, LNG (Liquefied NaturalGas) or the like is used as fuel to be ignited by a spark plug, forexample.

Main components of an engine system of the embodiment are illustratedschematically in FIG. 1, and a control block thereof is illustrated inFIG. 2, however, a valve mechanism for intake and exhaust, an EGRsystem, and the like are omitted for convenience. The engine 10according to the present embodiment is a compression-ignitionmulticylinder (four cylinders in the embodiment shown in FIG. 1)internal combustion engine that spontaneously ignites light oil,biofuel, or a mixture thereof as a fuel by injecting the fuel directlyinto a combustion chamber 12 in a compressed state through a fuelinjection valve 11. However, the engine 10 may be a single cylinderengine in connection with the characteristics of the present invention.The amount of fuel fed into the combustion chamber 12 through the fuelinjection valve 11 as well as injection timing are controlled by an ECU(Electronic Control Unit) 14 based on the position of an acceleratorpedal 13 pressed by a driver and the operating status of the vehicle.The amount that the accelerator pedal 13 is pressed is detected by anaccelerator position sensor 15, and the detected information isoutputted to an ECU 14 and used for setting an amount of fuel to beinjected from a fuel injection value 11.

An intake pipe 17 that is connected to an engine 10 by way of an intakemanifold 16, together with the intake manifold 16, defines an intakepassage 18, and on the upstream side and downstream side of the intakepipe 17, has a branched portion 19 d and a confluent portion 19 c withrespect to a branched intake pipe 19. In other words, both ends of thebranched intake pipe 19 are connected to the intake pipe 17 by way ofthe branched portion 19 d on the upstream side and the confluent portion19 c on the downstream side of the intake passage 18. That is to say, aportion of the intake pipe 17 that is located between the branchedportion 19 d on the upstream side and the confluent portion 19 c on thedownstream side of the intake passage 18, and the branched intake pipe19 are arranged in parallel. In the embodiment, a portion that isdefined by the branched intake pipe 19 is conveniently called a firstintake passage 18 f, and a portion that is defined by the intake pipe 17that is located between the branched portion 19 d on the upstream sideand the confluent portion 19 c on the downstream side of the intakepassage 18 is called a second intake passage 18 s.

An airflow meter 20 and an intake temperature sensor 21 are attached tothe intake pipe 17 further on the upstream side than the branchedportion 19 d on the upstream side of the intake passage 18, andinformation related to the intake flow and intake temperature that weredetected by these is outputted to the ECU 14. The ECU 14 performscorrection of the amount of fuel injection from the fuel injection valve11 based on the information detected from the airflow meter 20 and theintake temperature sensor 21.

An intercooler 22 that cools the intake in order to increase a filleddensity of the intake that flows through the intake passage 18, and athrottle valve 23 for adjusting an opening of the intake passage 18 areprovided in the intake pipe 17 further on the downstream side than theconfluent portion 19 c on the downstream side of the intake passage 18.The throttle valve 23 in the embodiment is mechanically linked to theposition of the accelerator pedal 13 that is adjusted by the amount thatthe driver presses the accelerator pedal 13, however, it is of coursepossible to employ a throttle valve that can electrically correct theopening according to the operating state of the vehicle.

An exhaust pipe 25 that is connected to the engine 10 by way of anexhaust manifold 24, together with the exhaust manifold 24, defines anexhaust passage 26, and has a branched portion 27 d and confluentportion 27 c related to a branched exhaust pipe 27 on the upstream sideand downstream side. In other words, both ends of the branched exhaustpipe 27 are connected to the exhaust pipe 25 at the branched portion 27d on the upstream side and the confluent portion 27 c on the downstreamside of the exhaust passage 26. That is to say, a portion of the exhaustpipe 25 that is located between the branched portion 27 d on theupstream side and the confluent portion 27 c on the downstream side ofthe exhaust passage 26, and the branched exhaust pipe 27 are arranged ina parallel state. In the embodiment, a portion that is defined by thebranched exhaust pipe 27 corresponds to a first exhaust passage 26 f ofthe present invention. Moreover, a portion that is defined by theexhaust pipe 25 that is located between the branched portion 27 d on theupstream side and the confluent portion 27 c on the downstream side ofthe exhaust passage 26 corresponds to a second exhaust passage 26 s inthe present invention.

A first exhaust turbine type turbocharger (hereinafter, referred to assimply a turbocharger) 28 is arranged so as to span between the firstintake passage 18 f and first exhaust passage 26 f, and the compressor28 a thereof being located in the first intake passage 18 f, the exhaustturbine 28 b is located in the first exhaust passage 26 f. Moreover, asecond turbocharger 29 that is mainly used in the low rpm range of theengine 10 more than the first turbocharger 28 is arranged so as to spanbetween the second intake passage 18 s and the second exhaust passage 26s. Together with a compressor 29 a of the second turbocharger 29 beinglocated in the second intake passage 18 s, an exhaust turbine 29 bthereof is located in the second exhaust passage 26 s. Therefore, thesecond exhaust passage 26 s that is branched off from the branchedportion 27 d on the upstream side goes around the exhaust turbine 28 bof the first turbocharger 28, passes through the exhaust turbine 29 b ofthe second turbocharger 29, and merges with the first exhaust passage 26f at the confluent portion 27 c on the downstream side. An exhaustemission purifier 30 is connected to the exhaust pipe 25 that is locatedfurther downstream than the confluent portion 27 c on the downstreamside of the exhaust passage 26.

An intake on-off valve 31 for opening or closing the first intakepassage 18 f is arranged in the first intake passage 18 f further on thedownstream side than the compressor 28 a of the first turbocharger 28.An on-off valve driving motor 32 is connected to the intake on-off valve31, and the ECU 14 controls the actuation of the on-off valve drivingmotor 32 according to the operating state of the vehicle, and switchesthe opening and closing operation of the intake on-off valve 31.Basically, when the engine speed, or in other words, the number ofrevolutions N_(n) per unit time of the engine is equal to or greaterthan the number of revolutions N_(R) (hereinafter, this will be referredto as fuel supply judgment speed) when the first turbocharger begins toexert a supercharging ability, the intake on-off valve 31 becomescompletely open. On the other hand, when less than the fuel supplyjudgment speed N_(R), the intake on-off valve 31 is controlled so as tobecome completely closed. In order for this, a crank angle phase of theengine 10 is detected by a crank angle sensor 33, and that detectioninformation is outputted to the ECU 14, after which the ECU 14calculates the engine speed N_(n) based on the information from thiscrank angle sensor 33.

A flow regulating valve 34 that can adjust the flow of exhaust thatflows in the first exhaust passage 26 f is arranged in the first exhaustpassage 26 f further on the upstream side than the exhaust turbine 28 bof the first turbocharger 28. Moreover, a valve position sensor 35 fordetecting the opening is connected to the flow regulating valve 34, andthe detection information is outputted to the ECU 14. An regulatingvalve driving motor 36, whose actuation is controlled by the ECU 14, isalso connected to the flow regulating valve 34, and the valve opening isadjusted based on the operating state of the vehicle and the detectioninformation from the valve position sensor 35. When fuel from a fuelsupply valve 38 of an exhaust heating apparatus 37 that will bedescribed later is supplied to the first exhaust passage 26 f, the flowregulating valve 34 is controlled so that the amount of exhaust flowingin the first exhaust passage 26 f becomes less than the amount ofexhaust flowing in the second exhaust passage 26 s. More specifically,the ECU 14, by way of the regulating valve driving motor 36, sets theopening of the flow regulating valve 34 so that exhaust flows in thefirst exhaust passage 26 at just a flow rate that the flame that iscaused to occur inside the first exhaust passage 26 f by the exhaustheating apparatus 37 does not go out. As a result, it is possible for apredetermined flow of exhaust by which the flame does not go out to flowin the first exhaust passage 26 f, and it is possible to lead theheating gas that is obtained by the exhaust heating apparatus 37 to theexhaust emission purifier 30.

The characteristics of the first and second turbochargers 28, 29 in theembodiment are illustrated in FIG. 3. The first turbocharger 28, havinga relatively large inertial mass, has hardly any supercharging abilityin the range where the engine speed N_(n) are equal to or less than thefuel supply judgment speed N_(R). On the other hand, the secondturbocharger 29, having a relatively small inertial mass, exertssupercharging ability from the range of low engine speed where the firstturbocharger 28 does not function. Therefore, when the engine speedN_(n) are equal to or less then the fuel supply judgment speed N_(R),the ECU 14 basically maintains the intake on-off valve 31 and flowregulating valve 34 in the completely closed state, and allows intakeand exhaust to flow through the second intake patch 18 s and secondexhaust passage 26 s. However, when it is necessary to supply fuel fromthe fuel supply valve 38 to inside the first exhaust passage 26 f, theECU 14 opens the flow regulating valve 34 a little so that part of theexhaust is led to the first exhaust passage 26 f.

The exhaust heating apparatus 37 is arranged in the first exhaustpassage 26 f located further upstream than the confluent portion 27 c ofthe first exhaust passage 26 f and second exhaust passage 26 s, andfurther downstream than the exhaust turbine 28 b of the firstturbocharger 28. This exhaust heating apparatus 37 is an apparatus forgenerating heated gas and supplying that heated gas to the exhaustemission purifier 30 located on the downstream side, and for activatingand maintaining the activated state of that exhaust emission purifier30. The exhaust heating apparatus 37 in the embodiment is provided inorder from the upstream side with the fuel supply valve 38, and a glowplug 39 that is used for ignition means in the present invention. In theembodiment, the first exhaust passage 26 f and an auxiliary oxidationcatalyst 40 are provided in that order from the upstream side betweenthe glow plug 39 and confluent portion 27 c.

The fuel supply valve 38 is for supplying fuel into the first exhaustpassage 26 f, and the ECU 14 controls a supply timing and a supplyamount based on the whether or not the exhaust emission purifier 30 isin the activated state and on the operating state of the vehicle.

The glow plug 39 is for igniting the fuel that is supplied from the fuelsupply valve 38 into the first exhaust passage 26 f. A direct-currentpower supply and a booster circuit (not illustrated in the figure) areconnected to the glow plug 39 in order to supply power thereto, and asurface temperature of the glow plug 39 is controlled by the ECU 14.Instead of a glow plug 39, it is also possible to use a ceramic heateror the like as a method of ignition of the present invention.

The operation of supplying fuel from the fuel supply valve 38 into thefirst exhaust passage 26 f, and heating of the glow plug 39 arebasically only performed when the engine speed N_(n) are equal to orless than the fuel supply judgment speed N_(R), and when the exhaustemission purifier 30 is in the non-activated state. However, as long asthe operating state is such that it is not necessary to lead exhaust tothe first exhaust passage 26 f, or in other words, when it is notnecessary to make the first turbocharger 28 to function, it is possibleto actuate the exhaust heating apparatus 37 with no problem. Moreover,when the exhaust emission purifier 30 and the auxiliary oxidationcatalyst 40 are activated, it is possible to actuate the exhaust heatingapparatus 37 as necessary even when the engine speed N_(n) are equal toor greater than the fuel supply judgment speed N_(R), or even when theoperating state is such that exhaust is led to the first exhaust passage26 f and the first turbocharger 28 is made to function.

The auxiliary oxidation catalyst is arranged in the exhaust passage 26between the glow plug 39 and the exhaust emission purifier 30. In theembodiment, this auxiliary oxidation catalyst 40 is arranged in theexhaust passage 26 f further on the upstream side than the confluentportion 27 c, however, it also could be arranged in the exhaust passage26 further on the downstream side than the confluent portion 27 c. Theauxiliary oxidation catalyst 40 has a cross-sectional area that is lessthan a cross-sectional area of the first exhaust passage 26 f, so partof the exhaust can pass without passing through the auxiliary oxidationcatalyst 40. In other words, a flow rate of the exhaust that passesthrough the auxiliary oxidation catalyst 40 is lower than a flow rate ofthe exhaust that does not pass through it, so it is possible to furtherraise a temperature of the exhaust that passes through the auxiliaryoxidation catalyst 40. When a temperature of the auxiliary oxidationcatalyst 40 is sufficiently high, or in other words, in the activatedstate, power to the glow plug 39 is cut, so it is also possible todirectly burn the fuel-air mixture inside the auxiliary oxidationcatalyst 40. However, when the auxiliary oxidation catalyst 40 is notactivated, such as at the time of the cold start of the engine 10, it isnecessary to supply power to the glow plug 39. When the temperature ofthe auxiliary oxidation catalyst 40 becomes high, hydrocarbons having alarge carbon number in the unburned mixture are broken down and reformedinto hydrocarbons having a small carbon number and high reactivity. Thatis to say, the auxiliary oxidation catalyst 40 on one hand functionsitself as a rapid heating element that heats at high speed, and on theother hand, also functions as a fuel reforming catalyst that generatesreformed fuel.

In this way, heated gas is generated in the first exhaust passage 26 f,and the high-temperature exhaust is then passed through the auxiliaryoxidation catalyst 40 and the temperature is further raised, and theunburned gas is either burned by the auxiliary oxidation catalyst 40, oris reformed to highly active hydrocarbon. Then, at the confluent portion27 c, these are mixed with the exhaust that is flowing in the secondexhaust passage 26 s and supplied to the exhaust emission purifier 30.As a result, it is possible to quickly activate and maintain theactivated state of the exhaust emission purifier 30. Particularly, thisexhaust heating apparatus 37 is extremely useful for improving theso-called cold emission state immediately after the cold start of theengine 10.

In order to increase the ignitability of the fuel that is injected fromthe fuel supply valve 38 into the first exhaust passage 26 f, providinga plate shaped vaporization promotion member that faces the fuel supplyvalve 38 and glow plug 39 is effective. This vaporization promotionmember has a function of scattering and atomizing fuel, or in otherwords promoting vaporization of fuel by colliding with fuel that isinjected from the fuel supply valve 38.

The exhaust emission purifier 30 is for detoxifying the toxic materialthat is generated by burning the fuel-air mixture inside the combustionchamber 12. The exhaust emission purifier 30 in the embodiment isprovided in order from the upstream side of the exhaust passage 26 withan oxidation catalyst 41, a three-way catalyst and a NOx catalyst,however, for convenience, only the oxidation catalyst 41 that isarranged on the most upstream end side is illustrated. In this oxidationcatalyst 41, incorporated is a catalyst temperature sensor 42 thatdetects a burner temperature and outputs that to the ECU 14.

The ECU 14 controls the flow regulating valve 34 and the exhaust heatingapparatus 37, or in other words, controls the actuation of the fuelsupply valve 38 and glow plug 39 according to a preset program and basedon the operating state of the vehicle and a detection signal from thecatalyst temperature sensor 42. In the embodiment, when, based on thedetection signal from the catalyst temperature sensor 42, a catalystelement temperature T_(n) is equal to or less than a T_(R) as anactivation index, it is determined that the exhaust emission purifier isnot activated. When the engine speed N_(n) are less than the fuel supplyjudgment speed N_(R) at which the first turbocharger 28 does not exertsupercharging ability, the flow regulating valve 34 is maintained in astate of being open a little, and part of the exhaust is also led to thefirst exhaust passage 26 f. Electric power is then supplied to the glowplug 39 and fuel is supplied from the fuel supply valve 38, and thetemperature of the exhaust that passes the exhaust turbine 28 b of thefirst turbocharger 28 is raised. However, when the catalyst elementtemperature T_(n) exceeds the activation judgment temperature T_(R), itis determined that the exhaust emission purifier 30 is activated, so thesupply of fuel from the fuel supply valve 38 is stopped, and the powerto the glow plug 39 is cut. Moreover, when the engine speed N_(n) areequal to or greater than the fuel supply judgment speed N_(R), at whichthe first turbocharger 28 exerts a supercharging ability, the intakeon-off valve 31 and the flow regulating valve 34 are maintained in thecompletely open state to allow the first turbocharger 28 to exert asupercharging effect. In this case, even when fuel is supplied from thefuel supply valve 38 into the first exhaust passage 26 f and ignited bythe glow plug 39, the flow rate of the exhaust that is flowing in thefirst exhaust passage 26 f is high, so there is a high possibility thatthe flame will go out. Therefore, in this case, the exhaust heatingapparatus 37 is not allowed to be actuated.

Such a control procedure of the exhaust heating apparatus 37 isillustrated in a flow chart in FIG. 4. In other words, in step S11 it isdetermined whether or not the temperature T_(n) of the oxidationcatalyst 41 that is detected by the catalyst temperature sensor 42 isequal to or less than the activation judgment reference temperatureT_(R). Here, when it is determined that the temperature T_(n) of theoxidation catalyst 41 is equal to or less than the activation judgmentreference temperature T_(R), or in other words, when it is determinedthat the oxidation catalyst 41 is in the non-activated state, processingmoves to step S12 and determines whether or not the engine speed N_(n)are equal to or greater than the fuel supply judgment speed N_(R). Here,when it is determined that the engine speed N_(n) are equal to or lessthan the fuel supply judgment speed N_(R), or in other words, when it isdetermined that the first turbocharger 28 does not exert anysupercharging ability, processing moves to step S13, and determineswhether or not a flag is set. At first, the flag is not set, soprocessing moves to step S14 and sets the flag, then in step S15electric power is supplied to the glow plug 39. Furthermore, in step S16the opening of the flow regulating valve 34 is adjusted so that part ofthe exhaust flows a little through the first exhaust passage 26 f, thenin step S17, fuel is injected from the fuel supply valve 38 into thefirst exhaust passage 26 f. As a result, fuel is ignited in the firstexhaust passage 26 f where a little exhaust is flowing, and atemperature of the heated gas that is obtained is further raised by theauxiliary oxidation catalyst 40. Then, at the confluent portion with thesecond exhaust passage 26 s, the gas is mixed with the exhaust thatflows from here, and is led to the exhaust emission purifier 30, whichraises the temperature of the exhaust emission purifier 30.

Next, in step S18, it is determined whether or not the temperature T_(n)of the oxidation catalyst 41 is greater than the activation judgmentreference temperature T_(R). Here, when it is determined that thetemperature T_(n) of the oxidation catalyst 41 is greater than theactivation judgment reference temperature T_(R), or in other words, whenit is determined that the oxidation catalyst is activated, processingmoves to step S19 and together with stopping the supply of fuel from thefuel supply valve 38, stops opening control of the flow adjustment value34. Then, depending on the engine speed N_(n), the flow regulating valve34 is switched to the completely closed state or completely open state.Furthermore, after the power to the glow plug 39 is stopped, processingmoves to step S20, resets the flag, and ends this series of control.

In step S18, when it is determined that the temperature T_(n) of theoxidation catalyst 41 is equal to or less than the activation judgmentreference temperature T_(R), or in other words, when it is determinedthat the oxidation catalyst 41 is not yet activated, processing returnsto step S12. Then it is determined whether or not the engine speed N_(n)are equal to or less than fuel supply judgment speed N_(R), and onlywhen the engine speed N_(n) are equal to or less than the fuel supplyjudgment speed N_(R), fuel is continuously supplied to the first exhaustpassage 26 f, and the oxidation catalyst 41 is activated. In step S13,the flat is set, or in other words, when it is determined that this isthe second time or later that fuel is supplied from the fuel supplyvalve 38, processing moves to step S17 and the supply of fuel continues.

In step S12, when the number of engine speed exceeds the fuel supplyjudgment speed N_(R), or in other words, when the first turbocharger 28is determined to be in a supercharging state, processing moves to stepS21 and determines whether or not the flag is set. Here, the flag isset, or in other words, when it is determined that this is the secondtime or later that fuel has been supplied from the fuel supply valve 38,processing moves to step S19 and stops the supply of fuel from the fuelsupply valve 38. Furthermore, opening control of the flow adjustmentvalue 34 is stopped, and the flow regulating valve 34 is switched to thecompletely open state. When the engine speed N_(n) exceed the fuelsupply judgment speed N_(R), the intake opening and closing value 31 isalso switched to the completely open state.

In step S21, when it is determined that the flag is not set, or in otherwords, when it is determined that fuel is not being supplied from thefuel supply valve 38, the control flow ends without doing anything.Moreover, in step S11, the same occurs when the temperature T_(n) of theoxidation catalyst 41 exceeds the activation judgment referencetemperature T_(R), or in other words, when it is determined that theoxidation catalyst 41 is activated.

In the embodiment described above, when the engine speed N_(n) are equalto or less than the fuel supply judgment speed N_(R), fuel is suppliedto the first exhaust passage 26 f. However, in the case of the operatingstate where the flow regulating valve 34 is closed so that exhaustcannot flow through the first exhaust passage 26 f, it is also possibleto perform control so that fuel is supplied to the first exhaust passage26 f. In this case, preferably, the flow regulating valve 34 is open alittle and exhaust is led to the first exhaust passage 26 f.

The present invention can also be applied to an engine system whereinthe first and second turbochargers 28, 29 described above are arrangedin series with respect to the exhaust passage 26. Another embodiment ofthe present invention is schematically illustrated in FIG. 5, and thesame reference numbers will be used for elements having identicalfunctions as those in the previous embodiment, however any redundantexplanations will be omitted. In other words, the intake pipe 17 thatdefines the intake passage 18 has a branched portion 43 d and aconfluent portion 43 c related to an intake bypass pipe 43 on theupstream side and downstream side of the intake pipe 17. That is, bothends of the intake bypass pipe 43 are connected to the intake pipe 17 bythe branched portion 43 d on the upstream side and the confluent portion43 d on the downstream side of the intake passage 18. That is to say, aportion of the intake pipe 17 that is located between the branchedportion 43 d on the upstream side and the confluent portion 43 c on thedownstream side of the intake passage 18, and the intake bypass pipe 43are arranged in parallel. In the embodiment, the intake passage 18 thatis further on the upstream side than the intake bypass pipe 43 is forconvenience called the first intake passage 18 f. Moreover, a portionthat is defined by the intake pipe 17 that is located between thebranched portion 43 d on the upstream side and the confluent portion 43c on the downstream side of the intake passage 18 is called the secondintake passage 18 s.

In the middle of the intake bypass pipe 43, an intake bypass valve 44for opening and closing the intake bypass pipe 43 is attached, and thatopening and closing operation is controlled by the ECU 14 by way of anintake bypass driving motor (not illustrated in the figure) according tothe operating state of the vehicle.

The exhaust pipe 25 that defines the intake passage 18 has a branchedportion 45 d and a confluent portion 45 c related to a first exhaustbypass pipe 45 on the upstream side and the downstream side of theexhaust pipe 25. In other words, both ends of the first exhaust bypasspipe 45 are connected to the exhaust pipe 25 by the branched portion 45d on the upstream side and the confluent portion 45 c on the downstreamside of the exhaust passage 26. That is to say, a portion of the exhaustpipe 25 that is located between the branched portion 45 d on theupstream side and the confluent portion 45 c on the downstream side ofthe exhaust passage 26, and the first exhaust bypass pipe 45 arearranged in a parallel state. The exhaust emission purifier 30 isconnected to the exhaust pipe 25 that is located further on thedownstream side than the first exhaust bypass pipe 45. The exhaust pipe25 that is located even further on the upstream side than the firstexhaust bypass pipe 45 further has a branched portion 46 d and aconfluent portion 46 c related to a second exhaust bypass pipe 46 on theupstream side and the downstream side of the exhaust pipe 25. In otherwords, both ends of the second exhaust bypass pipe 46 are connected tothe exhaust pipe 25 at the branched portion 46 d on the upstream sideand the confluent portion 46 c on the downstream side of the exhaustpassage 26. That is to say, a portion of the exhaust pipe 25 that islocated between the branched portion 46 d on the upstream side and theconfluent portion 46 c on the downstream side of the exhaust passage 26,and the second exhaust bypass pipe 46 are arranged in a parallel state.In the embodiment, a portion that is defined by the exhaust pipe 25 thatis located between the branched portion 45 d on the upstream side andthe confluent portion 45 c on the downstream side related to the firstexhaust bypass pipe 45 corresponds to the first exhaust passage 26 f inthe present invention. Moreover, a portion of the exhaust pipe 25 fromthe branched portion 46 d related to the second exhaust bypass pipe 46to the branched portion 45 d related to the first exhaust bypass pipe 45corresponds to the second exhaust passage 26 s in the present invention.

The first turbocharger 28 is arranged so as to span between the firstintake passage 18 f and the first exhaust passage 26 f, together withthe compressor 28 a thereof being located in the first intake passage 18f and the exhaust turbine 28 b being located in the first exhaustpassage 26 f. Moreover, the second turbocharger 29 that is mainly usedin a lower rotational speed range of the engine 10 than the firstturbocharger 28 is arranged so as to span between the second intakepassage 18 s and the second exhaust passage 26 s. The compressor 29 a ofthis second turbocharger 29 is located in the second intake passage 18s, and the exhaust turbine 29 b thereof is located in the second exhaustpassage 26 s between the branched portion 46 d and the confluent portion46 c related to the second bypass pipe 46. Therefore, the exhaustpassage 26 s that passes through the exhaust turbine 29 b of the secondturbocharger 29 goes around the exhaust turbine 28 b of the firstturbocharger 28 by way of the first exhaust bypass pipe 45, and mergeswith the first exhaust passage 26 f at the confluent portion 45 c on thedownstream side.

The exhaust heating apparatus 37 is incorporated in the second exhaustpassage 26 s further on the downstream side than the exhaust turbine 28b of the first turbocharger 28 and further on the upstream side than theconfluent portion 45 c that merges with the first exhaust bypass pipe45. Moreover, the exhaust emission purifier 30 is arranged in theexhaust passage 26 further on the downstream side than the confluentportion 45 c that merges with the first exhaust bypass pipe 45.

A first exhaust bypass valve 47 and a second exhaust bypass valve 48 areincorporated in the first exhaust bypass pipe 45 and the second exhaustbypass pipe 46, and make it possible to open and close these pipes. Theopening and closing operation of these valves is controlled by the ECU14 by way of a first exhaust bypass valve driving motor and a secondexhaust bypass valve driving motor (not illustrated in the figure). Inthe embodiment, an opening of the first exhaust bypass valve 47 can becontrolled so that part of the exhaust flows inside the second exhaustpassage 26 s, and in order for this, a valve position sensor 35 isattached to the first exhaust bypass valve 47. In other words, the firstexhaust bypass valve 47 corresponds to the flow regulating valve 34 inthe previous embodiment.

Therefore, when fuel is supplied from the fuel supply valve 38 to thefirst exhaust passage 26 f, the opening of the first exhaust bypassvalve 47 is controlled so that the flow of exhaust that flows throughthe first exhaust passage 26 f is less than the flow of exhaust thatflows through the second exhaust passage 26 s. More specifically, theopening of the first exhaust bypass valve 47 is controlled by the ECU 14by way of the first exhaust bypass valve driving motor so that exhaustflows through the first exhaust passage 26 f at just enough of a flowrate so that the flame that is caused to occur in the first exhaustpassage 26 f by the exhaust heating apparatus 37 does not go out.

The characteristics of the first and second turbochargers 28, 29 of theembodiment are illustrated in FIG. 6. The first turbocharger 28 that hasa relatively large inertial mass has hardly any supercharging ability inthe range where the engine speed N_(n) are equal to or less than thefuel supply judgment speed N_(R). However, the second turbocharger 29that has a relatively small inertial mass exerts supercharging abilityfrom the range of low engine speed where the first turbocharger 28 doesnot function. Therefore, when the engine speed N_(n) are equal to orless than the fuel supply judgment speed N_(R), the ECU 14 basicallymaintains the intake bypass valve 44 and the second exhaust bypass valve48 in the completely closed state, and maintains the first exhaustbypass valve 47 in the completely open state. Moreover, when the enginespeed N_(n) are greater than the fuel supply judgment speed N_(R), theECU 14 keeps the second exhaust bypass valve 48 in the completely closedstate. Furthermore, when the engine speed N_(n) are greater than asecond turbocharger stop judgment speed NS, the ECU 14 keeps the intakebypass valve 44 and second exhaust bypass valve 48 in the completelyopen state, and suppresses supercharging by the second turbocharger 29.

When it is necessary to supply fuel from the fuel supply valve 38 intothe first exhaust passage 26 f, the first exhaust bypass valve 47 isclosed a little from the completely open state, and part of the exhaustis led to the first exhaust passage 26 f. However, this operation isexecuted only when the first exhaust bypass valve 47 in the range wherethe engine speed N_(n) are equal to or less than the fuel supplyjudgment speed N_(R) is in the completely open state. As a result, fuelthat is injected into the first exhaust passage 26 f from the fuelsupply valve 38 is ignited by the glow plug 39, and without the flamegoing out, becomes heated gas and at the confluent portion 45 c thatmerges with the first exhaust bypass pipe 45, is mixed with the exhaustthat flows from the second exhaust passage 26 s. This promotesactivation of the exhaust emission purifier 30.

As described above, when there is no problem even though the fuelinjected from the fuel supply valve 38 may go out inside the firstexhaust passage 26 f, care must be taken in that the exhaust heatingapparatus 37 can be actuated in an arbitrary operating state.

It is to be noted that the present invention shall be construed solelyfrom the matters described in the claims thereof, and the foregoingembodiment includes not only the matters described above but any changesand corrections encompassed by the concept of the present invention. Inother words, all the matters in the foregoing embodiment are not tolimit the present invention, but include any configurations which maynot be directly related to the present invention and can be changedoptionally depending upon the application, purpose, and the like.

REFERENCE SIGNS LIST

-   10 Engine-   11 Fuel injection valve-   12 Combustion chamber-   13 Accelerator pedal-   14 ECU-   15 Accelerator position sensor-   16 Intake manifold-   17 Intake pipe-   18 Intake passage-   18 f First intake passage-   18 s Second intake passage-   19 Branched intake pipe-   19 d Branched portion-   19 c Confluent portion-   20 Airflow meter-   21 Intake temperature sensor-   22 Intercooler-   23 Throttle valve-   24 Exhaust manifold-   25 Exhaust pipe-   26 Exhaust passage-   26 f First exhaust passage-   26 s Second exhaust passage-   27 Branched exhaust pipe-   27 d Branched portion-   27 c Confluent portion-   28 First turbocharger-   28 a Compressor-   28 b Exhaust turbine-   29 Second turbocharger-   29 a Compressor-   29 b Exhaust turbine-   30 Exhaust emission purifier-   31 Intake on-off valve-   32 On-off valve driving motor-   33 Crank angle sensor-   34 Flow regulating valve-   35 Valve position sensor-   36 Regulating valve driving motor-   37 Exhaust heating apparatus-   38 Fuel supply valve-   39 Glow plug-   40 Auxiliary oxidation catalyst-   41 Oxidation catalyst-   42 Catalyst temperature sensor-   43 Intake bypass pipe-   43 d Branched portion-   43 c Confluent portion-   44 Intake bypass valve-   45 First exhaust bypass pipe-   45 d Branched portion-   45 c Confluent portion-   46 Second exhaust bypass pipe-   46 d Branched portion-   46 c Confluent portion-   47 First exhaust bypass valve-   48 Second exhaust bypass valve-   N_(n) Engine speed-   N_(R) Fuel supply judgment speed-   N_(S) Second turbocharger stop judgment speed-   T_(n) Catalyst element temperature-   T_(R) Activation judgment temperature

1.-10. (canceled)
 11. An exhaust heating apparatus for heating exhaustbeing led to an exhaust emission purifier from an internal combustionengine in which includes a first exhaust passage passing through anexhaust turbine of a first turbocharger and continuing to the exhaustemission purifier, a second exhaust passage being arranged in parallelwith the first exhaust passage, passing through an exhaust turbine of asecond turbocharger and continuing to the exhaust emission purifier, thesecond turbocharger being mainly used in a lower rotational speed rangeof the engine than the first turbocharger, and a valve being capable ofadjusting a flow of exhaust that flows in the first exhaust passage isarranged in the first exhaust passage further on the upstream side thanthe exhaust turbine of the first turbocharger, wherein the exhaustheating apparatus is arranged in the first exhaust passage that islocated further upstream than a confluent portion of the first andsecond exhaust passages being arranged in parallel between the engineand the exhaust emission purifier, and further downstream than theexhaust turbine of the first turbocharger.
 12. The exhaust heatingapparatus for the internal combustion engine as claimed in claim 11,wherein the exhaust heating apparatus comprises a fuel supply valve forsupplying fuel to the first exhaust passage, and ignition means forigniting and burning fuel that was supplied from the fuel supply valveto the first exhaust passage.
 13. The exhaust heating apparatus for theinternal combustion engine as claimed in claim 12, wherein an oxidationcatalyst is arranged in the exhaust passage between the ignition meansand the exhaust emission purifier.
 14. The exhaust heating apparatus forthe internal combustion engine as claimed in claim 11, wherein when fuelis supplied to the first exhaust passage from the fuel supply valve, anopening of the valve is adjusted so that the flow of exhaust flowing inthe first exhaust passage becomes less than a flow of exhaust that flowsin the second exhaust passage.
 15. A control method for the exhaustheating apparatus as claimed in claim 11, comprising the steps of:detecting a rotational speed of the internal combustion engine; andflowing a predetermined amount of exhaust in the first exhaust passageand actuating the exhaust heating apparatus when the detected rotationalspeed of the engine is equal to or less than a predetermined rotationalspeed, or when in an operating state where the first exhaust passage canbe shut off.
 16. An exhaust heating apparatus for heating exhaust beingled to an exhaust emission purifier from an internal combustion enginein which includes an exhaust passage passing through an exhaust turbineof the first turbocharger and continuing to the exhaust emissionpurifier, a first exhaust bypass going around the exhaust turbine of thefirst turbocharger and continuing to the exhaust passage, a firstexhaust bypass valve being capable of adjusting a flow of exhaust thatflows in the first exhaust bypass, a second exhaust bypass that isarranged in parallel with respect to the exhaust passage being locatedfurther upstream than the first exhaust bypass so that the secondexhaust bypass goes around an exhaust turbine of a second turbochargerthat is mainly used in a lower rotational speed range of the engine thanthe first turbocharger, the exhaust turbine of the second turbochargerbeing arranged in the exhaust passage further on the upstream side thanthe first exhaust bypass, and a second exhaust bypass valve beingcapable of adjusting a flow of exhaust that flows in the second exhaustbypass, wherein the exhaust heating apparatus is arranged in the exhaustpassage that is located further upstream than a confluent portion of theexhaust passage and the first exhaust bypass, and further downstreamthan the exhaust turbine of the first turbocharger.
 17. The exhaustheating apparatus for the internal combustion engine as claimed in claim16, wherein the exhaust heating apparatus comprises a fuel supply valvefor supplying fuel to the exhaust passage, and ignition means forigniting and burning fuel that was supplied from the fuel supply valveto the exhaust passage.
 18. The exhaust heating apparatus for theinternal combustion engine as claimed in claim 16, wherein an oxidationcatalyst is arranged in the exhaust passage between the ignition meansand the exhaust emission purifier.
 19. The exhaust heating apparatus forthe internal combustion engine as claimed in claim 16, wherein when fuelis supplied to the exhaust passage from the fuel supply valve, theopening of the first exhaust bypass valve is adjusted so that the flowof exhaust that flows in the exhaust passage becomes less than the flowof exhaust that flows in the first exhaust bypass.
 20. A control methodfor the exhaust heating apparatus as claimed in claim 16, comprising thesteps of: detecting a rotational speed of the internal combustionengine; and flowing a predetermined amount of exhaust toward the exhaustturbine of the first turbocharger when the detected rotational speed ofthe engine is equal to or less than a predetermined rotational speed, orwhen in an operating state where the first exhaust bypass can be fullopened.